Homosexuality is mysterious: we do not really know what it is. It is politically correct to see it as an innate genetic thing like skin colour, but this is untenable. For it is possible for a heterosexual to experience homosexual desire, or to have an active homosexual phase. Also, it is clear enough that nurture plays a huge role in the formation of sexuality, and that our very concept of homosexuality is culturally determined.

Our idea of homosexuality is a rather recent invention. In our narrative, a young adult discovers that he or she is different, and announces his or her commitment to this different identity. Coming out is a bit like a pledge: this is not a phase, but who I am; I commit myself to this identity.

Every previous culture to our own would have seen it as odd, this insistence that homosexuality is a fixed identity, which one discovers within one's soul, and sticks to. To the ancient Greek, homosexuality was something you might do for a while, like playing football, or seeing a shrink. This was a freer idea of sexuality. We like to think we are the most liberated imaginable culture, but actually our narrative of homosexuality suggests otherwise: we demand that homosexuality is penned in by this idea of either-or identity. We have opted to tolerate "identity homosexuality" instead of temporary homosexuality and bisexuality, which are potentially more threatening to the dominant sexual order (the '"straightus-quo"?).

Because this development is so recent, it makes little sense to say that ancient Israelite culture was "anti-gay". It also makes little sense to say that ancient Greek culture was gay-friendly. For neither culture shared our idea of what homosexuality is. In fact these ancient cultures agreed more with each other than either does with us. For both saw homosexuality as a form of behaviour rather than an innate identity. To the ancient Jew, it was a disgustingly self-indulgent bit of behaviour, inextricable from hedonistic promiscuity, and a befouling of the sacred bond of marriage. To the Greek citizen, it was no big deal; just a facet of (male) human desire.

So the real question is: how should Christians respond to the fact that the Bible condemns homosexual behaviour? Is it legitimate simply to reassert this condemnation, to say that it still stands? No, for two reasons. First, the meaning of homosexuality has changed. In the new narrative of homosexuality, a gay person is just as inclined to seek stable monogamy as a straight person. The Bible's assumption that gay sex is a form of indulgence unrelated to marriage can no longer be shared.

Secondly, Christians are not committed to following the rules laid down in the Bible. They reject the need for circumcision and food laws. And all moral laws. St Paul said that we have to break the link between God's will and religious laws. We have to make up morality as we go, putting love and freedom first. Ah, but didn't St Paul clearly condemn gay sex? Yes, but this is because he shared the general biblical view, that it was inextricable from hedonism. Christians who use Paul to condemn homosexuality have failed to grasp Paul's key message: that holy rules are dead.

So the answer to this question has two parts. Yes, the Bible condemns homosexual behaviour, as a threat to moral order. But the New Testament condemns something else as well: holy moralism. It announces an anti-legalistic revolution. It tells us we have to keep our moral thinking mobile, open-ended. The Bible sows the seed of the deconstruction of its own sexual moralism.